The present invention relates to a so-called throttle valve for controlling an amount of suction air supplied to an interal combustion engine of an automotive vehicle or the like and, more particularly, to an electronically controlled type throttle valve for internal combustion engines, in which an opening degree of the throttle valve is controlled electronically through an actuator.
For a gasoline engine of an automotive vehicle, or the like, for example, there are various severe demands on running controllability, exhaust gas characteristics, fuel consumption characteristics and so on. In view of these severe demands, in recent years, there is such a tendency as to employ the following system. That is, an opening degree of a throttle valve is controlled in mechanically interlocked relation to an accelerator pedal, as has conventionally been employed widely. In addition thereto, various data required for controlling the engine, including the operating condition of the accelerator pedal, are once inputted to an electronic control system composed of, for example, a microcomputer or the like. Subsequently, the opening degree of the throttle valve is controlled on the basis of a control signal from the electronic control system through a predetermined electric actuator. Specifically, a system has already been proposed in, for example, Japanese patent application Laid-Open No 61-229935 or the like, in which an actuator operated by a DC motor is used to effect control of opening and closing of the throttle valve.
A system is also known from, for example, in Japanese patent application Laid-Open No. 62-129529 or the like, in which a stepping motor is utilized as a driving source, and rotational force of the driving stepping motor is transmitted to a shaft of the throttle valve through a reducing gear mechanism.
In the electronically controlled type throttle valve of the kind referred to above, the electric motor or the like serving as the actuator is driven in response to an amount of change of the accelerator pedal and, in addition thereto, the throttle valve can be corrected and controlled in accordance with the running conditions of the engine. Thus, the throttle valve has such an advantage that the running controllability of the engine can be raised.
By the way, the conventional electronically controlled type throttle valve described above employs a system in which a so-called butterfly valve having a so-called single disc mounted on a shaft for rotation is used, and the butterfly valve is drivingly operated by the electric actuator mounted on the outside of the throttle body.
In the butterfly valve described above, however, the requisite operational torque varies considerably depending upon the throttle opening degree or an angle of the valve. This is due to torque produced by air flowing through the throttle body. In addition, the above-mentioned butterfly valve is provided with a return spring for returning the valve always toward the fully closed position. By this return spring, the operational torque required for controlling the opening degree of the butterfly valve is brought to a considerably large value. This raises such problems that it is made difficult to reduct the capacity of the electric actuator for generating the operational torque, it is made difficult to reduce the size the throttle body, and it is made difficult to accommodate the throttle valve in the engine room which has such a recent tendency as to be reduced more and more.